STERRHA SACRARIA. 115 



in Exeter I find they did not enjoy such a favourable 

 time for their development. Throughout September 

 and October, 1865, the thermometer stood several 

 degrees higher than in the same months of this year, 

 with the exception of one frosty night in October ; 

 and as 8. sacraria is believed to have its head-quarters 

 in climates much warmer than our own, we may suppose 

 that the greater success of the former brood is thus 

 accounted for. At the same time, if we allow that 

 cold is so fatal to S. sacraria, we are met by the 

 question, How then can it establish itself at all in this 

 country ? For we can scarcely suppose that the 

 specimens taken year by year are fresh immigrants, or 

 the offspring of immigrants which arrived in time to 

 secure sufficient warm weather for the perfecting of 

 their broods. 



However, one point has been fairly settled this year, 

 and that is a more correct description of the larvae. 

 From notes taken by Mr. Llewelyn and myself it 

 seems that nearly every individual of the whole brood 

 of twenty-five presented some little peculiarity of its 

 own, but that all might be fairly ranged under three 

 main varieties. 



Var. 1. I have taken for the type the form which 

 has all the characteristic markings, yet without any 

 exaggeration in the colouring. Ground colour on the 

 back a soft delicate grey, on the belly a greenish-white ; 

 dorsal line paler than the ground, very finely but dis- 

 tinctly edged with blackish threads, which become 

 stronger on segments 10 to 12; the subdorsal line 

 also pale with fine edgings, and on segments 1 to 

 5 having a strong dark streak immediately below it, 

 continued backwards as a dark thread. Sometimes 

 the edgings of the lines are not so dark, but have a 

 reddish tint; sometimes again the dorsal line is not of 

 uniform width, but at the fold from segments 5 to 10 

 opens into a small white dot, immediately followed by a 

 small black dot, which thus interrupts the line. 



Yar. 2. On one side of the type comes the variety 



